Combinations of an activating cation and a weakly coordinating borate anion are used as components of metallocene olefin polymerization catalysts. Procedures for preparation of the borate anion portion of such combinations are described in the prior art. See European patent applications Nos. 505,972 and 505,997, Japanese published patent application No. 63-238057, and PCT International Application WO 94/00459.
Grignard reactions are conventionally conducted in an ether solvent. U.S. Pat. No. 5,473,036 describes the reaction of a fluorophenyl Grignard with a boron trihalide in an ether solvent to produce a magnesium halide salt of a tetrakis-fluorophenyl borate. The patent states: "The ether is needed to solubilize the Grignard reagent, fluorophenyl magnesium bromide" (Col. 2, 11. 1-2). The magnesium halide is converted by cation exchange to a different tetrakis-fluorophenyl borate salt to provide a borate anion useful in metallocene catalyst synthesis.